October 23, 2012 

EVALUATION OF INADVERTANT INGESTION OF RADIONUCLIDES
 

DCAS’ RESPONSE TO SC&A’S EVALAUTION OF TIB-009
 

Background 

The current approach to estimating ingestion intakes for workers without bioassay 

monitoring data is described in DCAS Technical Information Bulletin 009 (OCAS-TIB009). This TIB, which has been used to estimate ingestion intakes during both the 

operational and residual contamination periods, relies on ambient air concentration 

measurements to estimate the amount of daily ingestion in the workplace. Specifically, 

TIB-009 estimated that the total daily ingestion is equal to 20% of the activity contained 

in one cubic meter or air1

. The model in TIB-009 was originally reviewed by SC&A in 

June of 2006 (SC&A 2006). In their review, SC&A commented that the model was 

likely to produce intakes that are too low and unrealistic. The basis for this opinion was 

provided in the following findings that were included in their evaluation report. 

•	 Surface contamination levels are likely to be orders of magnitude higher than 

predicted by the settling velocity of airborne contaminants assumed at 5 microns. 

For example, at uranium rolling mills, airborne particulates are likely to represent 

a distribution of particles that range from a few microns to large/visible particles. 

For larger particles, settling velocities increase dramatically and while large 

particles limit internalization by inhalation, there are no limitations for their 

ingestion. 

•	 Surface contamination is likely to build up over time that may extend to 

weeks/months or longer before reaching equilibrium. NIOSH’s assumption that 

this equilibrium is reached in a 24-hour period is without scientific basis and 

highly unconservative. 

•	 For select processes, surface contamination may not be the result of settling, but 

may include liquid spills, or result from milling, grinding, cutting, welding, etc. 

•	 The modeled transfer of surface contaminations to the mouth that assumes a 10% 

transfer from the surface area of one hand during a full workday appears 

unrealistic. In a hot/dusty work environment, a “radiologically 

uninformed/untrained” worker is likely to contact/wipe his/her face with both 

hands repeatedly over the course of a full workday. 

•	 Ingestion may involve other modes such as direct deposition on lips, smoking of 

cigarettes, etc. 

Inadvertent ingestion in TIB-009 does not apply to the intake of radioactive material that is inhaled and 

subsequently removed from the lungs to the gastrointestinal tract. This mode of ingestion is included in the 

IRCP’s respiratory tract model. 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its Working Groups 

or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their technical 

support and review contractors) positions unless specifically marked as such. This document represents preliminary positions 

taken on technical issues prepared by NIOSH or its contractor. 

NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 USC §552a 

and has been cleared for distribution. 

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NIOSH has reviewed the above findings and concurs that the parameters used in the TIB009 model are based on assumptions that have not been empirically demonstrated to be 

valid. The main concerns expressed in SC&A’s findings center on two issues: 1) the 

possible lack of an association between measured air concentrations in the workplace and 

surface contamination, and 2) the modeled transfer of the surface contamination to the GI 

tract through inadvertent ingestion. 

Characterization of the relationship between air and surface contamination levels 

To evaluate the relationship between air contamination and surface contamination levels, 

NIOSH reviewed the available air and surface contamination measurement at Simonds 

Saw and Steel and Bethlehem Steel. At Simonds Saw Steel these measurements were 

taken during a uranium rolling campaign on 10/27/48 and were direct measurements 

made with a portable instrument called a Zeuto2

. This type of instrument has an active 

surface area that is 3 inches by 4 inches or approximately 75 cm2. The Bethlehem Steel 

data, available for a rolling on 9/14/1952, were obtained by smears wiped over a 100 cm2 

area. As such, they represent only the removable portion of the contamination. Each 

rolling stand at both Bethlehem Steel and Simonds Saw were evaluated along with the 

shear at Bethlehem Steel. Stand #6 at Bethlehem Steel was not evaluated because the 

surface smear indicated no detectable activity. Where more than one sample was taken, 

the results were averaged. 

Subsequent to the analysis of the Bethlehem Steel and Simonds Saw and Steel data, 

NIOSH found paired surface contamination and air concentration data at two additional 

facilities. The first of these were collected at Superior Steel during a test rolling on 

5/13/53. The air data was collected at one of the finishing rollers while the smear was 

collected 20 feet east of the roller. 

The second set of data was found at the Vitro Manufacturing facility in Canonsburg, 

Pennsylvania. Between 8/18 and 8/20 of 1953, a series of air sample and contamination 

smears were collected by representatives of the Health and Safety Laboratory (HASL). 

In all, approximately 240 air samples and 150 contamination smears were collected at 

various locations within the plant. These data were entered into an EXCEL spreadsheet 

and the distributions of the data were characterized. Because both data sets were found to 

be log-normally distributed, the geometric mean and standard deviation was calculated 

for each set. 

Table 1 provides the air and surface contamination measurements for the facilities 

described above. 

2 As a direct measurement device, the Zeuto quantifies total activity that would include both fixed and 

loose contamination. As loose contamination is the only type of material that contributes to ingestion, the 

use of this value would provide an overestimate of the source term available for the ingestion pathway. 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its Working Groups 

or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their technical 

support and review contractors) positions unless specifically marked as such. This document represents preliminary positions 

taken on technical issues prepared by NIOSH or its contractor. 

NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 USC §552a 

and has been cleared for distribution. 

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Table 1 – Air and Surface Contamination Values 

Air sample reference Air concentration 

(dpm/m3

) 

Surf. Contamination location Surf. Contamination value 

(dpm/100 cm2) 

Simonds Saw Data 

L709 49000 

L710 75000 east roller 1 50000 

L711 22400 west roller 1 35000 

Average 48800 Average 42500 

L718 14800 

L719 23800 

L720 27900 

L721 943 

L722 836 

L723 418 west roller 2 15000 

average 11449.5 Average 15000 

Bethlehem Steel Data 

Q921 2076 

Q922 2973 Shear 679 

Q923 1080 Shear 404 

Average 2043 Average 541.5 

Q903 3 

Q905 10 Stand 1 2 

Average 6.5 Average 2 

Q906 10 

Q908 12 Stand 2 9 

Average 11 Average 9 

Q909 18 

Q911 14 Stand 3 6 

Average 16 Average 6 

Q912 13 

Q913 10 

Q920 6 Stand 4 5 

Average 9.7 Average 5 

Q914 12 

Q915 3 

Q919 12 Stand 5 9 

Average 9 Average 9 

Superior Steel Data 

SRDB 6898 (pages 4-6) 7600 Finish roll #5 1140 

Vitro Manufacturing 

SRDB #104483 and 10450 GM = 25.3 Plant-wide GM = 68.0 

3 Samples are from pages 1-18 of SRDB #10448. Control samples and blanks and several samples without 

an indicated flow-rate were omitted from analysis. 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its Working Groups 

or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their technical 

support and review contractors) positions unless specifically marked as such. This document represents preliminary positions 

taken on technical issues prepared by NIOSH or its contractor. 

NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 USC §552a 

and has been cleared for distribution. 

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The values for each pair of air concentration and surface contamination values are plotted 

in Figure 1. The clear trend can be seen in Figure 1 that empirically demonstrates the 

measured surface contamination levels are proportional to air contamination. It is also 

worthy of note that this relationship is internally consistent at Simonds Sam and Steel and 

Bethlehem Steel. That is, high airborne activity is predictive of high surface 

contamination levels and vice versa. This means that if any large particle surface 

contamination that does not add to the air concentrations exists, the fraction of surface 

contamination represented by this is consistent across locations and sites and 

concentrations. 

Figure 1 – Graph of observed air concentration and surface contamination levels Surface Contamination (dpm/100 cm2) 

100000 

10000 

1000 

100 

10 

1 

1 10 100 1000 10000 100000 

Air Concentration (dpm/m3) 

A linear regression analysis was performed on the dataset plotted in Figure 1 and the 

following results were obtained4: 

Sc = 116.7 ∗ Am

r2 = 0.96

where Sc = the estimated level of surface contamination in dpm/m2

, and 

Am = the measured air concentration in dpm/ m3. 

Given that there is a relationship between air concentration and surface contamination 

level, it should be possible to use air concentration values to estimate ingestion intakes. 

4 Since surface concentration should be zero in the presence of no airborne activity, the data were analyzed 

with the intercept set through the origin. 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its Working Groups 

or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their technical 

support and review contractors) positions unless specifically marked as such. This document represents preliminary positions 

taken on technical issues prepared by NIOSH or its contractor. 

NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 USC §552a 

and has been cleared for distribution. 

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The only other factor required to establish this relationship is the daily ingestion rate for 

loose surface contamination. 

Evaluation of the daily ingestion rate 

The model put forth in TIB-009 assumes that there are two modes of ingestion – one 

from the ingestion of material that had settled onto a drinking container and one from the 

ingestion of material that was transferred to the hand and subsequently to the mouth. 

While the scenario modeled in TIB-009 seems plausible to NIOSH, it is acknowledged 

that neither of the assumptions used in the model are based on peer reviewed studies of 

the work habits of individuals. 

The NRC computer program RESRAD-BUILD (NRC 2002) does, however, contain an 

ingestion parameter that is based on an extensive review and analysis of the literature 

surrounding this intake pathway. In this model, ingestion of radionuclide contamination 

in the workplace is directly related to the amount of loose surface contamination present. 

If the amount of loose surface contamination per unit area is known, a worker’s hourly 

ingestion rate can be calculated as follows: 

lh = C ∗ m GO

where Ih = the hourly ingestion rate in dpm/h; 

Cm = the surface contamination measured in the workplace in dpm/m2

; and 

GO = the effective transfer rate for ingestion of removable contamination in m2/h. 

The value for GO used in the RESRAD model is represented by a log-uniform 

-5 -4 2 -4 distribution with values between 2.8x10 and 2.9x10 m /hr and a mean of 1.1x10

m

2

/hr. Although the value for GO was originally considered a constant when it was 

developed in volume 1 of NUREG/CR-5512 (NRC 1992), it was subsequently updated to 

a log-normal distribution in Volume 3 (NRC 1999). In volume 3, there was an attempt to 

correlate ingestion intakes with soil ingestion studies that had recently been published. 

The mean ingestion rate for the adult studies corresponded to an ingestion of 50 mg/day 

which would correspond to a worker ingesting 100 cm2 of contaminated surface per hour. 

This value was considered by the authors to be implausibly high and the use of soil 

ingestion study data to set the upper limit was abandoned. In the end, the average value 

of 1.1 x 10-4 

m

2

/hr (corresponding to an ingestion of about 0.5 mg/day) was considered to 

represent the average member of the screening group and was said to define the default 

value for GO. The corresponding ingestion rate for an 8 hour work day would be 8.8 x 

10-4 m2/d. 

The difficulty of applying this parameter to the facilities covered under the Energy 

Employees Occupational Illness Compensation Program Act is that very few 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its Working Groups 

or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their technical 

support and review contractors) positions unless specifically marked as such. This document represents preliminary positions 

taken on technical issues prepared by NIOSH or its contractor. 

NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 USC §552a 

and has been cleared for distribution. 

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measurements of surface contamination exist in situations where ingestion levels must be 

estimated (i.e., those facilities where bioassay measurement data cannot be used to 

estimate total intake). This is especially true for Atomic Weapons Employer (AWE) 

facilities during the residual contamination period. 

Tying together air concentration, surface contamination, and ingestion 

Given that a relationship has been established between air concentration values and 

surface contamination levels, and a default value for daily ingestion has been identified, it 

is possible to evaluate workplace ingestion based solely on air concentration data. This 

can be expressed as follows: 

l� = 116.7 ∗ A ∗ GO m

l� = 0.103 ∗ A (1) m

where Id = the daily ingestion of loose radioactive material in dpm/d, 

Am = the measured air concentration in the workplace in dpm/m3, and 

GO = the NUREG/CR-5512 default for ingestion in the workplace in m2/d 

= 8.8 x 10-4 

m

2

/d. 

As discussed previously, TIB-009 guidance is to estimate daily ingestion intake using the 

following relationship: 

l� = 0.2 ∗ Am (2) 

where Id = the daily ingestion rate in dpm/day; and 

Am = the air concentration measured in the workplace in dpm/m3. 

Discussion 

It can be seen that the intakes based on empirical data and mean value for GO (equation 

1) would predict ingestion intakes that are almost exactly half of that of the approach 

based on TIB-009 (equation 2). Thus, even though the parameters and assumptions used 

in TIB-009 were somewhat simplistic, the model nonetheless produces estimates of 

ingestion that are in reasonable agreement with the NUREG predictions. It should also 

be considered that the 20% multiplier used in TIB-009 includes an ingestion source term 

for a contaminated beverage or food item. This type of ingestion was not considered in 

the development of GO in the NUREG. Given the uncertainty inherent in the values 

discussed above, it is not unreasonable for NIOSH to continue using the TIB-009 

approach for estimating intakes. 

It should also be mentioned that the ingestion exposure pathway results in doses that are 

quite small compared to inhalation exposure. Under the TIB-009 approach, ingestion 

will always be a fraction of the inhalation exposure (i.e., 1 dpm/m3 of air activity will 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its Working Groups 

or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their technical 

support and review contractors) positions unless specifically marked as such. This document represents preliminary positions 

taken on technical issues prepared by NIOSH or its contractor. 

NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 USC §552a 

and has been cleared for distribution. 

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result in the assignment of daily inhalation and ingestion exposures of 9.6 dpm and 0.2 

dpm/day, respectively). In addition, for uranium intakes (for which TIB-009 is almost 

exclusively applied), the uptake across the gastrointestinal tract is low. This combination 

of factors results in the ingestion pathway contributing less than 0.6% to the dose for soft 

tissues under all solubility types5. The maximum contribution for ingestion would be, as 

expected, to organs of the gastrointestinal tract. For these organs, the highest 

contribution to a dose is 3.4% for lower large intestine when insoluble material (ICRP 

type S) is inhaled. 

Application of TIB-009 during residual contamination periods 

Based on a recent review of the approach adopted for estimating ingestion intakes at the 

Dupont Deepwater Works (DCAS-TBKS-0006), it has been discovered that TIB-009 has 

been improperly applied during the residual contamination period. For periods of time 

after the cessation of AEC activities, it is inappropriate to use a resuspension factor to 

estimate an air concentration and then multiply that value by 0.2 to calculate a daily 

ingestion intake. The reason for this is that the relationship between air concentration 

and surface activity in TIB-009 assumes an active source or process is generating the 

airborne activity. The airborne activity predicted using a resuspension factor of, for 

example 1 x10-6/m, would grossly under represent the airborne activity that actually 

deposited the surface contamination. For TIB-009 to be applied during residual 

contamination periods, the air concentration on the first day of the residual contamination 

period should be assumed to be equal to that which was present during the end of 

operations. The ingestion calculated in this manner can then be decreased over time 

using the source depletion techniques described in TIB-0070. 

A review of several TIBs has revealed that this error is not isolated to the Dupont 

Deepwater works. A comprehensive review of the estimation of ingestion during the 

residual contamination period will be conducted for all TIBs. As errors are discovered, 

the TIBs will be revised and a program evaluation report (PER) will be issued. 

5 Assuming a chronic inhalation exposure over a one year period. 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its Working Groups 

or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their technical 

support and review contractors) positions unless specifically marked as such. This document represents preliminary positions 

taken on technical issues prepared by NIOSH or its contractor. 

NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 USC §552a 

and has been cleared for distribution. 

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References 

Sanford Cohen and Associates, SCA-TR-Task 3 Supplement 1. June 2006. Review of 

NIOSH/ORAUT Procedures and Methods Used for Dose reconstruction, pages 89-93. 

NRC. 1992. Residual Radioactive Contamination from Decommissioning. NUREG/CR5512 Vol. 1. 

NRC. 1999. Residual Radioactive Contamination from Decommissioning – Parameter 

Analysis. NUREG/CR-5512 Vol. 3. 

NRC. 2002. Technical Basis for Calculating Radiation Doses for the Building 

Occupancy Scenario Using the Probabilistic RESRAD-Build 3.0 Code. NUREG/CR6755. 

This is a working document prepared by NIOSH or its contractor for use in discussions with the ABRWH or its Working Groups 

or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final NIOSH or ABRWH (or their technical 

support and review contractors) positions unless specifically marked as such. This document represents preliminary positions 

taken on technical issues prepared by NIOSH or its contractor. 

NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 USC §552a 

and has been cleared for distribution. 

8